A large variety of lubricants and hydraulic fluids contain triaryl phosphates. These compounds are relatively stable so that the phosphate ester fluids have long service life. However, over long periods of time organophosphate fluids undergo chemical degradation accompanied by higher acid content. Such increased acidity may eventually lead to systemic corrosion.
Numerous methods have been devised for reclaiming used organophosphate functional fluids. However, each of the prior art methods suffers from one or more serious limitations making it less than entirely suitable for its intended purpose.
Anzenberger U.S. Pat. No. 4,402,883 describes a method for reducing acidity in used organophosphate functional fluids. The method comprises contacting a used fluid with any of several types of activated alumina, returning treated fluid to the system for reuse, and subsequently regenerating the activated alumina. The disclosure of said Anzenberger patent is incorporated herein by reference, to the extent consistent with the present invention.
In the prior art, various molecular sieves other than Y zeolite have been used as adsorbents for acids. However, these adsorbents have poor adsorption kinetics and adsorption capacities. In addition, they are expensive and can be chemically degraded by the acids. Pure Y zeolites are particularly unsuitable for use as acid adsorbents because they are so readily attacked.
Some patents disclosing adsorbents based upon combinations of alumina and molecular sieves include Figert U.S. Pat. No. 3,025,233; Chi et al U.S. Pat. No. 3,899,310; Michel U.S. Pat. No. 3,917,544; Minachev et al U.S. Pat. No. 3,764,563; and Podschus British Pat. No. 1,491,563. None of these patents discloses the use of a composite alumina/Y zeolite adsorbent for adsorbing acids or moisture from organophosphate functional fluids.
It is a principal objective of the present invention to provide a method for reducing the acidity and moisture content of used organophosphate functional fluids, utilizing a novel solid composite adsorbent.
Additional objects and advantages of the invention will become apparent to persons skilled in the art from the following specification and claims.